Institutional environments such as hospitals and nursing homes, hotels, banquet halls, and the like all have food service operations that require the use of devices to maintain the prepared food warm after its preparation and before service. Generally, the kitchen for these types of places is in a location that is remote from the patients or people and thus the food needs to be transported from the remote location to the patients or people. In many instances the length of time between the preparation of the food and the serving of the food may be upwards to one hour. In some cases, it has been found desirable to prepare the meals well in advance of serving.
Obviously, it is desirable to maintain the heated food warm until it is served. To this end, there have been developed essentially three types of devices for maintaining the food warm from the time of preparation until the time of service. One way is termed rethermalization. In rethermalization the food is placed on plates on a tray, with the tray placed within a metal cabinet. The cabinet includes heating pads for each tray that correspond in location to the food to be heated on the tray. The entire meal is placed on the tray with a plurality of trays stored in the cabinet. The cabinet is stored in a refrigerator unit until it is time to reheat and serve the meal. A heater control coupled to the cabinet and heating pads is activated to heat only the food on the warming pads thereby keeping the remaining food cold. The heating is accomplished while the cabinet is within the refrigerator unit. Once the rethermalization cabinet has been removed from the refrigerator unit, there is no more heating of the food. Therefore, depending on the time out of the refrigerator and the distance to each and the last patient, the food can cool down. Therefore, such cabinets are of limited effectiveness.
Another way is to provide an insulated container, generally consisting of an insulated base or tray with an insulated cover therefore. A plate with heated food is placed on the previously insulated base with the cover placed thereover. The heat from the heated food maintains the food warm within the insulated cover. These devices are effective for generally short periods of time and only moderately effective for longer periods of time.
Yet another type of device in use is a heatable base that is likened to a heat sink. This type of device is effective when all of the food on the plate is to be kept warm. The base is heated to a sufficient temperature whereupon a plate with prepared food is placed upon the heated base and a cover placed thereover. The base is placed in a convection type heating unit or oven to sufficiently heat the base. The core of the base includes what is known as a phase change material that absorbs heat when heated, and which slowly dissipates the heat thereafter. The dissipating heat is transmitted to the plate situated thereon to keep the food warm. Generally, a cover is placed over the plate that mates with the base.
Prior art heatable bases have included such phase change materials as pure wax, solid phase change materials, and bladders carrying such materials. In the prior art these bases have been manufactured from plastic and stainless steel. Such bases are exemplified in the following U.S. Pat. Nos.: 2,876,634 issued Mar. 10, 1959 to Zimmerman et al.; 3,054,395 issued Sep. 18, 1962 to Torino; 3,065,744 issued Nov. 27, 1962 to Scavallo; 3,148,676 issued Sep. 15, 1964 to Truog et al; 3,557,774 issued in 1969 to Kreis; 3,837,330 issued Sep. 24, 1974 to Lanigan et al; 3,875,370 issued Apr. 1, 1975 to Williams; 4,059,096 issued Nov. 22, 1977; 4,086,907 issued May 2, 1978 to Rothschild; 4,246,884 issued Jan. 27, 1981 to Vandas; 4,505,252 issued Mar. 19, 1985 to Wada et al; 4,567,877 issued Feb. 4, 1986 to Sepahpan; 4,777,931 issued Oct. 18, 1988 to Ziegler et al; 4,982,722 issued Jan. 8, 1991 to Wyatt; and 5,125,391 issued Jun. 30, 1992 to Srivastava et al. However, stainless steel is quite objectionable in that stainless steel transfers its heat at a much quicker rate than plastic. Also, all of these bases must be heated by a convection type oven or heating unit which generally takes a fair amount of time to raise the temperature of the core of the base to a sufficient temperature. Furthermore, plastic is air permeable, which over time allows air to penetrate into the phase change material which reduces the life expectancy or use of the phase change material and the base. Also, such high convection temperatures that are necessary to raise the core to a proper temperature for maintenance of a specific low end or minimum temperature for a specific period of time anneals the plastic causing the plastic to become brittle and fail.
It is apparent from the foregoing that the prior art food warmers are deficient in many respects. Thus, it is an object of the present invention to provide a heat retentive base for food plates that reduces the time necessary to sufficiently heat the base.
It is another object of the present invention to provide a food service base whose operation is not affected by time, air permeability, or repeated use cycling.